Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!ucbvax!TOPS20.RADC.AF.MIL!GUBBINS
From: GUBBINS@TOPS20.RADC.AF.MIL (Gern)
Newsgroups: comp.sys.zenith.z100
Subject: Re: NEC chips
Message-ID: <12549565305.9.GUBBINS@TOPS20.RADC.AF.MIL>
Date: 12 Dec 89 19:01:08 GMT
References: <8912121507.AA23004@ll-vlsi.arpa>
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Our Reliablity and Testability Division will differ with that.   A NEC V20
10MHz will function in a 10MHz Z-100 and only crash once or twice in a few
hours.   Z-100 Diagnostics will report TOTAL RAM failure (obviously boarderline
as the Diag program is running), pushing the NEC V20, a NEC 8284A, a NEC
74LS240/241/244 Bus driver in a 10.7MHz Z-100, the system will crash usually
in under 20 minutes on the average in under 10 minutes.   There is no problems
at all with Intel/Siemans/AMD 8088-1 and all other non-NEC ICs.  This is
the only configuration I can recommend.

I have done a lot of testing in Z-100 speed-up.   I bought the NEC V20 at 
the time as the fastest Intel 8088 was 8MHz.  I have since become biased
against them only after seeing their parts consistantly be the problem
in Z-100 speedup or Z-100 IC failures (5 or 8MHz machines).  Try it:
Take a 256Kx1 DRAM 8MHz ZDS factory or HA-108 upgrade new motherboard Z-100
and change the 24MHz crystal to 32MHz.   Power it up and the system will
be dead without even a Meep.   Replace whatever brand of 8MHz 8088 with
a non-NEC 8088-1 (10MHz), power up, if there are NEC ICs on the motherboard
except perhaps the keyboard controller, the system will have problems and
usually fail diagnostics.  If there are no NEC ICs or you replace them,
the Z-100 will run at 10.7MHz very happily forever and pass diagnostics
(except RS-232 and floppy which is a fault of the Diagnostic program), but
RAM diagnostics will pass and the system is rock solid.  Since you now have
a rock solid stable 10.7MHz Z-100, replace the 8088-1 with a 10MHz V20
and you now have a flakey system that will not pass RAM and other diagnostics.

I have done this to two Z-110s and a friend to one.  I have had the same
results with a 32MHz (10.7MHz Z-100) and 30MHz (10.0MHz Z-100, ie. CPUs
'in spec').   The same results for all three Z-100s: A solid 10.7MHz only
with non-NEC parts (DRAM too), sorry, but that is the results.

As a side note, benchmarking the NEC V20 against an 8088, MHz per MHz, the
V20 was faster by 6% at all speeds, the Norton SI showed a 25% increase
but this is due to the well known SI bias toward 80186/286 architecture.
The benchmarks do not take into account getting a Z-100 with a V20 to
not crash long enough to complete a benchmark.

As a side-side note, an 8088 (5MHz) run at 8MHz will start off operating
for about 30 minutes before it crashes, then each cool-down, repower-up
will run about 10 minutes less until it won't run long enough to boot,
replacing the 8088 with another at 5MHz is consistant.   I toasted five
8088 (5MHz) running at 8MHz, 30 minutes of reliability each before the
8088-2 (8MHz) arrived.

Cheers,
Gern
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